This invention relates to compositions useful for cleaning metal surfaces. More particularly, the invention relates to water-based compositions which in addition to cleaning the surface of metals when applied thereto also have other desirable properties which make them highly useful for industrial metal-working applications.
The need to clean the surface of metals subsequent to various metal working operations is well known. For example, parts obtained from machining operations are cleaned to remove metal fines, residual cutting oil, dirt. etc. Similarly the surface of metal sheet obtained from rolling operations is generally cleaned after the final reduction and prior to the application of slushing oils or coating oils which are employed to protect the surface of the metal sheet during coiling and subsequent storage. In tandem mills where the metal sheet is continuously passed in one direction through multiple stands which progressively reduce the thickness of the metal, the last stand is primarily employed to impart the desired surface quality to the metal, i.e., smooth, polish and clean the metal surface. It is at this point in the rolling operation where cleaners are applied to the metal to remove any residual rolling oil, dirt and scale. After the cleaning operation the metal sheet is coiled for shipment or storage. If a slushing or coating oil is required to protect the metal during shipment/storage, the protective oil is applied after the cleaning step and before coiling.
Highly alkaline detergent solutions (pH 9.5 or higher) have been used almost exclusively as cleaners. These typically contain alkali phosphates, alkali carbonates, alkali silicates, caustic soda or combinations thereof in conjunction with a surfactant. for example, a composition suitable as a metallic cleaning agent comprised of water, a Group IA or IIA metal hydroxide and at least one sulfur-containing compound selected from trimethylene ring sulfur compounds, mercapto alkanones and dialkylaminoalkyl dithiocarbamic acids are disclosed in U.S. Pat. No. 4,400,312. Sulfur-based aqueous metal cleaners are similarly employed in U.S. Pat. No. 4,421,667. The cleaners of U.S. Pat. No. 4,421,667 contain 80-99.5 weight percent water, 0.1-5 weight percent water soluble surfactant, 0.1-5 weight percent Group IA or IIA metal hydroxide and 0.25-10 weight percent thiomorpholine compound. The cleaning and degreasing compositions of U.S. Pat. No. 4,421,680 contain potassium hydroxide and sodium metasilicate pentahydrate in combination with n-butoxyethanol, coconut diethanolamide, cocamidopropyl betaine, isopropylamine salt of dodecylbenzenesulfonic acid and water.
Due to the problems associated with handling and disposal of highly alkaline metal cleaning materials, there is a need for products which are effective for degreasing and cleaning metal surfaces but which do not include strongly alkaline detergents. One such product, comprised of an aqueous solution containing 3-20 parts fatty acid sucrose ester, 3-15 parts polyoxyethylene alkyl ether, 1-10 parts chelating agent, 1-5 parts petroleum sulfonate and 3-10 parts propylene glycol, is described in U.S. Pat. No. 4,395,365. The products of U.S. Pat. No. 4,395,365 are considerably less alkaline (pH about 8 to 8.5) and utilize organic surface-active agents which are harmless to the human body and can be decomposed by microorganisms. The inclusion of a chelating agent also imparts some rust- and corrosion-inhibiting ability to the cleaners of U.S. Pat. No. 4,395,365.
U.S. Pat. No. 3,870,647 discloses concentrated liquid detergent cleaners containing propylene glycol, a small amount of monoethanolamine, fatty acids and ethoxylates. The cleaners are primarily useful as laundry detergents but also suggested to be useful for the removal of oils and greases and for cleaning hard surfaces.
It would be highly advantageous if other aqueous compositions having moderate pH and which are effective cleaners for metal surfaces were available. It would be even more advantageous if the cleaners also provided a non-greasy and non-sticky protective barrier on the surface of the metal to prevent rust and corrosion during storage and shipping. These and other advantages are realized with the improved multi-purpose metal cleaning compositions of the present invention.